1. Field of the Invention
The present invention relates to a television system, and more particularly, to an apparatus and method for correcting jitter which can be generated by truncation during the processing of an internal signal and by asynchronization between the television system and an external system.
2. Description of the Related Art
The function of displaying an analog RGB video signal output from a computer on a cathode ray tube (CRT) using a television system is typically performed by a multimedia television. In such a system, there is a horizontal synchronous signal and a vertical synchronous signal in addition to the RGB video signal in the information transferred from the computer to the television system. These external horizontal synchronous and vertical synchronous signals are typically not synchronized with a system clock signal (CLK) used for the television system.
Jitter can be generated on the screen of the CRT by the external synchronous signals as described below with reference to the attached drawings. FIG. 1 contains four waveforms labelled (a) through (d) related to an Nth horizontal scan line of the CRT screen. Waveform (a) illustrates a horizontal synchronous signal in asynchronous relation with a system clock signal illustrated in waveform (c). Waveform (b) shows an RGB video signal. Waveform (d) shows a waveform of the horizontal synchronous signal synchronized with the system clock signal (CLK) of waveform (c).
The horizontal synchronous signal of waveform (a) and the RGB video signal of waveform (b) are applied from the computer to the television system with a time difference of Td1 as shown. Then, when the horizontal synchronous signal of waveform (a) is synchronized the system clock signal (CLK) of waveform (c), the time difference between the horizontal synchronous signal and the RGB video signal changes from Td1 to Td2 as shown in waveform (d).
FIG. 2 contains four waveforms labelled (a) through (d) related to an (N+1)th horizontal scan line of the CRT screen. Waveform (a) shows the horizontal synchronous signal in asynchronous relation with the system clock signal (CLK) shown in waveform (c). Waveform (b) shows the waveform of the RGB video signal. Waveform (d) shows the horizontal synchronous signal synchronized with the system clock signal (CLK) of waveform (c).
In the (N+1)th horizontal scan line displayed on the CRT subsequent to the Nth horizontal scan line, the horizontal synchronous signal and the RGB video signal respectively shown in waveforms (a) and (b) are applied from the computer to the television system with a time difference of Td3. Then, when the horizontal synchronous signal of waveform (a) is synchronized with the system clock signal (CLK) of waveform (c), the time difference between the horizontal synchronous signal and the RGB video signal changes from Td3 to Td4 as shown in waveform (d).
As mentioned above, the time difference between the horizontal synchronous signal and the RGB video signal changes whenever the horizontal synchronous signal is input from the personal computer to the television system. Therefore the time difference varies in every horizontal scan line, and, as a result, the image displayed on the CRT exhibits vertical jitter.
Also, in such a system, a digital phase difference and a digital interpolation value between a fly back pulse (FBP) and a horizontal driving signal are typically truncated in a signal processing process. Specifically, in the typical television system, only the upper bits of the digital interpolation value and the digital phase difference are used, and the lower bits are truncated. The resulting truncation error causes vertical jitter on the image displayed on the CRT. The jitter components deteriorate picture quality and can cause viewers"" eyes to tire.
It is an object of the present invention to provide an apparatus for correcting jitter of a television system by which it is possible to correct jitter components which can be induced by a synchronous signal applied externally and by a truncation error in a television system.
It is another object of the present invention to provide a method for correcting jitter of a television system performed in the jitter correcting apparatus of the television system.
Accordingly, the invention is directed to an apparatus and method for correcting jitter of a television system. The television system includes a horizontal driving signal generator for generating a horizontal driving signal in response to a system clock signal and a first synchronous signal. In one embodiment, the invention includes a first phase difference detecting portion for detecting a first phase difference between the system clock signal and a second synchronous signal, the second synchronous signal being (i) an external input to the television system, (ii) asynchronous with the system clock signal, and (iii) able to be set as the first synchronous signal. A jitter correcting portion of the invention corrects a jitter component included in the horizontal driving signal in response to the first phase difference and outputs a horizontal driving signal with a corrected jitter component.
In accordance with the invention, a method for correcting jitter of a television system performed by the jitter correcting apparatus of the television system having a horizontal driving signal generator for generating a horizontal driving signal in response to a system clock signal and a first synchronous signal includes detecting a first phase difference between a second synchronous signal and the system clock signal, wherein the second synchronous signal is (i) asynchronous with the system clock signal and (ii) able to be set as the first synchronous signal. In accordance with the invention, the method also includes correcting the jitter component included in the horizontal driving signal, corresponding to the first phase difference.